1. Field of Invention
The present invention concerns an ink composition used suitably in a ink jet recording method, a recording method for recording images using the same, as well as an ink set and an ink head.
2. Description of the Related Art
An ink jet recording method is a typical non-impact recording method of discharging and flying liquid droplets of an ink composition (hereinafter also referred to simply as “ink”) by using a kinetic energy or thermal energy and depositing liquid droplets on a recording material such as paper thereby recording images. The ink jet recording method has advantages that noises during recording are reduced compared with an impact recording method, the size of the apparatus can be decreased easily since development and fixing processes indispensable, for example, in electrophotographic recording method are not required and high speed recording is possible. Among the ink jet recording method, an on demand type ink jet recording method of discharging ink droplets in response to digital signals are relatively inexpensive in view of the apparatus and color processing is easy compared with a continuous ink jet recording method of continuously discharging ink droplets, so that this is generally used in recent years as output equipments for office equipments or personal computers for home use.
An ink jet recording apparatus for recording images by using an ink jet recording method is required for providing recording images at high image quality comparable with recording images by electrophotographic recording process at high speed and stably. Further, durability such as water proofness and light fastness are required for the formed recording images.
As a technique for improving the water proofness and light fastness of recorded images, a method of using a pigment for a colorant contained in an ink has been studied. While the most general method is a method of dispersing a pigment in an ink, since the particle size of pigment particles in the ink is large and the pigment tends to be precipitated in this method, it involves a problem of tending to cause clogging at the top end of a nozzle for discharging ink droplets and not capable of providing recorded images stably.
In recent years, the problem for the precipitation of the pigment has been solved along with the development of the dispersion technique. When images are formed on a recording material having feel of gloss nearly to that of printed paper photography referred to as gloss paper as one of recording sheets used in an ink jet recording method, it results in an additional problem that the pigment ingredient from the recording material.
Further, when recorded images formed by using an ink in which a pigment is dispersed is traced by a pen using an aqueous ink such as a marker pen, this results in a problem that recorded images are blurred or pigment is peeled from the recording material to disturb the recorded images.
For example, in Japanese Examined Patent Publication JP-B2 2635235 is disclosed an ink with an improved dispersion stability of a pigment in the ink by using an AB or ABA block copolymer of a hydrophobic block A and a hydrophilic block B. However, recorded images formed by using the ink are poor in the scratch resistance leading to a practical problem such as defoliation of the pigment ingredient from the recording material.
In order to solve the foregoing problems, the ink in which the pigment is dispersed is required to provide recorded images of excellent water proofness and scratch resistance in addition to stable dispersion of the pigment into the ink.
For example, in Japanese Examined Patent Publication JP-B2 3122405 is proposed a technique of improving the water proofness and scratch resistance of recorded images without deteriorating the dispersion stability of a pigment. In this technique, in order to improve the water proofness and scratch resistance, a water soluble elastomeric block polymer ABA comprising an elastomeric block B and a non-elastomeric block A is incorporated.
However, while the technique disclosed in Japanese Patent No. 3122405 is effective in the case of using a recording material with rough surface having large inter-fiber distance such as common paper, sufficient scratch resistance can not be obtained in the case of using a recording material with smooth surface having a coating layer containing fine particles disposed on the upper surface thereof.